06 scion xb, sound system

Hello guys/gals.

I'm in the process of installing an intermediate level sound system in my car and had just one quick question.

The vehicle its going in is an 06 scion xb

Im using only Alpine components...here's what it consists of:

Alpine CDA-9856 Head Unit

Alpine SPS-17C2 6.5" coaxials front and back

Alpine SPS-10C2 4" coaxial speakers to replace factory dash tweeters

Alpine SWR-1242D 12" DVC sub

Alpine MRP-F250 4 Channel amp for mids/highs

Alpine  MRP-M650 Mono amp for lows

Now, time for the question...

I read in the Alpine HU's manual that when an external amp is used and the pre-amp outputs are occupied, that It would de-activate the HU's internal amp. This is causing some concern because I planned on powering the 4'' dash speakers with the HU which are only rated at 2-30 watts RMS, making it difficult to wire them in with the 6.5" coaxials. Especially since the amp will put out 50x4 @ 2 ohms.

Am I missing something? Do I have any other options besides buying another small 2 ch amp, or am I completely off here?

Any and all input is greatly appreciated.

Please go easy on me, I'm still learning.

Thanks for your response.

So, what you're saying is that the internal HU amplifier does not automatically become disabled when the pre-outs are used?

I would like to use the HU to power my 4" coaxials. Can anyone please confirm this?